Firstly, mother cat is a ginger tabby and female gingers are rare - male ginger cats outnumber female gingers by 3 to 1.
Secondly, mom was trapped as a feral and all 5 of her kittens are also gingers. The chances of that happening in a feral cat environment are also very rare.
I took this picture at a local shelter and I was told that momcat gave birth to the kittens on top of an ivy-covered wall and the kittens all started falling through the ivy and were found on the ground and brought to the shelter owner, who struggled with bottle-feeding a litter of five newborns. She told the people who brought the kittens to do whatever they could to find the mother. A few days later, this lactating female was trapped nearby to where the kittens were born. She was brought in to the shelter and accepted the kittens as her own. They are 99.9% sure that this cat is the mother and everyone was very relieved that she decided to accept her kittens after a few days away from them. Although mother cats often do feed kittens that aren't theirs, there was always the chance that she would reject them.